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Killed some of my fish. Help!!

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Hi,

I am a new aquarium owner and, it seems, not a very good one.

I got a 5 gallon tank and stocked it with washed gravel, 2 fake plants, a heater with a thermostat, 5 gallons of spring water treated with water conditioner and bacteria supplement. After doing all this, I added 5 1" fish. Everything looked good for about 3 weeks and all of a sudden I find 4 dead fish. The remaining fish isn't looking too good, but I'm hoping that he will survive.

I did some water tests with my API test kit and found the following:

amonia 4ppm
ph 6.6
nitrite 0ppm
Nitrate 0ppm

I took the following corrective action:

Removed the dead fish
Put Ammo Chips in my filter
Removed 40% of the water and put in new treated water

Is there anything else I should do and can do to prevent this happening again and to save my remaining 1 fish? How long should I wait before attempting to add more fish?

5 inch in fish? Of which species? I'd say that's quite densely stocked for a 5 gallon. I get the impression you've been working on store supplied information. If you do that then the results like you get are fairly typical.

At the moment your ammonia is at toxic high levels. Your levels indicate that there's no beneficial bacteria in your tank. There's several pieces of information here on fishless cycling, read those. If you want to attempt to save the last fish start doing 50% changes daily.

The reason for all your bad luck is that you haven't cycled your tank. In a healthy, established tank, it isn't the filter media that is most important, but the beneficial bacteria that grows on it and converts nitrite and ammonia(produced by decomposing fish waste) into the less harmful nitrate which is removed through water changes. Cycling a tank essentially is the process of accumulating these bacteria to make the tank healthy for fish.

First off, you should remove your ammo chips. They may be a lifesaver over the short term, but if you leave them in while trying to cycle, they will absorb all the ammonia and prevent any cycle from happening. After that, you will have to closely monitor your ammonia, nitrite and nitrate levels. You should have some ammonia in your tank to keep the cycle going, but it must not exceed 0.25 ppm because levels higher than that are acutely toxic(as you must have already experienced). Control ammonia levels by doing water changes. You can do this with normal tap water instead of spring water by the ways. Eventually your ammonia should drop to zero and nitrites will appear. Again, use water changes to keep nitrites under 0.25 ppm. Once your nitrites drop to zero and nitrates start appearing, you have completed your cycle. Nitrates will remain nitrates(doesn't get converted to anything) and must be kept under 20 ppm through water changes.

After that, add fish one by one to prevent an overload of your bacterial filter.

You asked: "Won't changing that much water pretty much guarantee that no biological filter can take hold?"
As long as you keep Ammonia at .25 in the water, you will start growing beneficial bacterial. the water does not hold your beneficial bacteria. The filter and filter media hold the BB. you only need enough ammonia in the water at this stage to help that bb grow and .25 will do it. Eventually, you'll grow enough to kill the ammonia and the nitrites (that will come) and you'll have 0 readings on both.
It's going to take patience and water changes.
Good luck

After 3 weeks you should be reading some nitrite and nitrate as well as the ammonia. What sort of filter do you have and how do you clean it and how often?

When I go fishing I just throw sharp rocks in the water and wait for the dead fish to float to the top... KingfisherEverything happens for a reason. Sometimes that reason is you are stupid and make bad decisions. I think my fish is adjusting well to the four gallon, He's laying on his side attempting to go to sleep on the bottom of the gravel.
A moderator on a fish forum should be able to identify an oscar... Don't you think?Dear naps, sorry I hated you so much when I was a child... Love me